1. Field of the Invention
The present invention relates to the treatment of vascular disease, and more particularly to a removable, variable-diameter vascular filter system for use during medical procedures.
2. Discussion of Related Art
Percutaneous transluminal coronary angioplasty (PTCA), stenting and atherectomy are therapeutic medical procedures used to increase blood flow through the coronary arteries. These procedures can often be performed as alternatives to coronary bypass surgery. PTA (percutaneous transluminal angioplasty) and stenting can often be performed as alternatives to carotid endarterectomy, and femoral-popliteal bypass procedures. In PTA or PTCA procedures, the angioplasty balloon is inflated within the stenosed vessel, at the location of an occlusion, in order to shear and disrupt the wall components of the vessel to obtain an enlarged lumen. In stenting, an endoluminal prosthesis is implanted in the vessel to maintain patency following the procedure. In atherectomy, a rotating blade is used to shear plaque from the arterial wall.
One concern commonly encountered in all these techniques is the accidental release of portions of the plaque, thrombus or other embolic particulates, resulting in emboli which can lodge elsewhere in the vascular system. Such emboli may be extremely dangerous to the patient, and may result in myocardial infarction, stroke or limb ischemia.
In order to initiate these procedures, one must first introduce a guidewire into the lumen of the vessel to serve as a conduit for other interventional devices, such as angioplasty balloons and stent delivery systems. This guidewire must be advanced into a position past the location of the occlusion. Guidewires must be capable of traversing tortuous pathways within the body, consisting of bends, loops and branches. For this reason, guidewires need to be flexible, but they should also be sufficiently stiff to serve as a conduit for other devices. In addition, they must be xe2x80x9ctorqueablexe2x80x9d to facilitate directional changes as they are guided into position. Guidewires are well known in the art, and are typically made of stainless steel, tantalum or other suitable materials, in a variety of different designs. For example, U.S. Pat. Nos. 4,545,390 and 4,619,274 disclose guidewires in which the distal segment is tapered for greater flexibility. The tapered section may be enclosed in a wire coil, typically a platinum coil, which provides increased column strength and torqueability. Another design is identified in U.S. Pat. No. 5,095,915, where the distal segment is encased in a polymer sleeve with axially spaced grooves to provide bending flexibility.
Vascular filters are also well known in the art, especially vena cava filters, as illustrated in U.S. Pat. Nos. 4,727,873 and 4,688,553. There is also a substantial amount of medical literature describing various designs of vascular filters and reporting the results of clinical and experimental use thereof. See, for example, the article by Eichelter and Schenk, entitled xe2x80x9cProphylaxis of Pulmonary Embolism,xe2x80x9d Archives of Surgery, Vol. 97 (August, 1968). See, also, the article by Greenfield, et al, entitled xe2x80x9cA New Intracaval Filter Permitting Continued Flow and Resolution of Emboli""xe2x80x9d, Surgery, Vol. 73, No. 4 (1973).
Vascular filters are often used during a postoperative period, when there is a perceived risk of a patient encountering pulmonary embolism resulting from clots generated peri-operatively. Pulmonary embolism is a serious and potentially fatal condition that occurs when these clots travel to the lungs. The filter is therefore typically placed in the vena cava to catch and trap clots before they can reach the lungs.
Many of the vascular filters in the prior art are intended to be permanently placed in the venous system of the patient, so that even after the need for the filter has passed, the filter remains in place for the life of the patient. U.S. Pat. No. 3,952,747 describes a stainless steel filtering device that is permanently implanted transvenously within the inferior vena cava. This device is intended to treat recurrent pulmonary embolism. Permanent implantation is often deemed medically undesirable, but it is done because filters are implanted in patients in response to potentially life-threatening situations.
To avoid permanent implantation, it is highly desirable to provide an apparatus and method for preventing embolization associated with angioplasty, stenting or other procedures. In particular, it is desirable to provide a device which can be temporarily placed within the vascular system to collect and retrieve plaque, thrombus and other embolic particulates which have been dislodged during angioplasty, stenting or other procedures. Such a device is removed at the end of the procedure. U.S. Pat. Nos. 5,814,064 and 5,827,324 describe such a device, wherein the filter is expanded to a predetermined diameter through the introduction of a fluid or a gas. U.S. Pat. No. 5,910,154 describes a filter, which expands to a predetermined diameter through the use of a spring-based actuator. U.S. Pat. No. 6,053,932 describes a filter, which expands to a predetermined diameter through the use of a cinch assembly.
One concern commonly encountered with all these devices is that the filter opens to a single, predetermined diameter, thereby requiring an inventory of filters of different diameters, so as to insure that the proper size is available for the patient.
The prior art makes reference to the use of alloys such as Nitinol (Nixe2x80x94Ti alloy), which have shape memory and/or superelastic characteristics, in medical devices that are designed to be inserted into a patient""s body. The shape memory characteristics allow the devices to be deformed to facilitate their insertion into a body lumen or cavity, and then, when heated within the body, to return to their original shape. Superelastic characteristics, on the other hand, generally allow the metal to be deformed and restrained in the deformed condition to facilitate the insertion of the medical device containing the metal into a patient""s body, with such deformation causing the phase transformation. Once within the body lumen, the restraint on the superelastic member can be removed, thereby reducing the stress therein so that the superelastic member can return to its original un-deformed shape by the transformation back to the original phase.
The prior art makes reference to the use of metal alloys having superelastic characteristics in medical devices which are intended to be inserted or otherwise used within a patient""s body. See for example, U.S. Pat. No. 4,665,905 (Jervis).
Some guidewire designs have recommended the use of superelastic alloys. For example, U.S. Pat. No. 4,925,445 discloses a guidewire where the distal segment, and at least one portion of the proximal segment, is made from a superelastic alloy like Nitinol, where the transformation temperature from austensite to martensite occurs at 10xc2x0 C. or below. Also, U.S. Pat. No. 4,984,581 discloses a guidewire having a core of shape memory alloy, where the shape memory properties of the alloy provide both tip-deflection and rotational movement in response to a controlled thermal stimulus.
However, the prior art has yet to disclose any guidewires, made from Nitinol or other suitable materials, incorporating removable, variable-diameter vascular filters, which can be used to address the clinical problem of collecting and retrieving portions of plaque, thrombus or other embolic particulates which have been dislodged during angioplasty, stenting or other procedures.
The present invention provides for a removable, variable-diameter vascular filter system which can be used to capture portions of plaque, thrombus or other embolic particulates dislodged during angioplasty, stenting or other procedures, and which overcomes many of the deficiencies associated with the prior art devices, as briefly described above.
In accordance with one aspect, the present invention is directed to a removable, variable-diameter vascular filter system comprising a guidewire having an outer diameter and an inner diameter, a proximal end and a distal end; a generally solid core wire having an outer diameter, a proximal end and a distal end, with the distal end slidably inserted into the proximal end of the guidewire, and advanced through the guidewire until the distal end of the core wire extends beyond the distal end of the guidewire; an end cap attached to the proximal end of the core wire; a spacer having a proximal end and a distal end, with the spacer removably mounted onto the core wire in a longitudinal direction such that the proximal end of the spacer is substantially in contact with the end cap; and a filter, comprising a proximal end and a distal end, a plurality of struts extending therebetween, and a porous covering permanently attached to the struts, with the proximal end of the filter attached to the distal end of the guidewire, and the distal end of the filter attached near the distal end of the core wire; the filter having a smaller first diameter for insertion into a vessel, and a larger second diameter for expanding to substantially equal the diameter of the lumen of the vessel and to be placed in a generally sealing relationship with the lumen of the vessel. The filter is placed distal to the occlusion to collect embolic particulates released during the medical procedure.
The advantage of the present invention is that the spacer can be used to vary the diameter of the filter, so that a single device can be used to capture embolic particulates in vessels of different lumenal diameters. In addition, the present invention eliminates the need for delivery sheaths, capture sheaths, and an inventory of systems with different diameter filters.